In recent years, demand for flat panel displays having characteristics such as a thin profile, low weight, and low power consumption has rapidly increased.
Generally, an LCD includes two substrates, each of which has an electrode on one surface thereof. The substrates are disposed such that the surfaces with the electrodes face each other. The LCD displays an image by controlling the light transmission of a liquid crystal material disposed between the two substrates. The transmision is varied when a voltage is applied to the electrodes due to changes in the degree of rotation of liquid crystal molecules in the material.
Various types of LCDs can be fabricated. Active matrix LCDs (AM-LCD), in which thin film transistors (TFTs) and pixel electrodes connected to the TFTs are arranged in a matrix configuration, is popular due to its superior resolution and capability of reproducing moving pictures.
In the AM-LCD, a lower array substrate has pixel electrodes formed thereon, and an upper color filter substrate has a common electrode thereon. Therefore, as a voltage is applied to the electrodes of the array substrate and the color substrate, a vertical electric field is formed between the two substrates to rotate the liquid crystal molecules. The AM-LCD has advantages, such as superior transmittance and aperture ratio, and also prevents liquid crystal cells from failing due to static electricity because the upper common electrode serves as a ground.
The upper color substrate further includes a black matrix for preventing light leakage at a portion other than the pixel electrodes.
Meanwhile, the lower array substrate is formed by repeated processes of depositing thin films and patterning the deposited thin films by photolithography using a mask. In the patterning of the deposited thin films, five or six masks are generally used. The number of masks used generally corresponds to the number of processes used for fabricating the array substrate.
A related art array substrate for an LCD and fabrication method thereof will now be described with reference to the accompanying drawings.
FIG. 1 is a plan view of an array substrate for an LCD according to a related art, and FIG. 2 is a sectional view taken along the line I-I′ of FIG. 1.
Referring to FIGS. 1 and 2, the array substrate for an LCD includes a transparent insulating substrate 110, a gate line 121 formed on the transparent insulating substrate 110 in a horizontal direction, and a gate electrode 122 extending from the gate line 121.
A gate insulator 130 is formed on the gate line 121 and the gate electrode 122, and an active layer 141 and an ohmic contact layer 151, 152 are sequentially formed on the gate insulator 130.
A data line 161 perpendicularly crossing the plurality of gate lines 121, a source electrode 162 extending from each of the data lines 161, a drain electrode 163 spaced apart from the source electrode 162 on the gate electrode 122, and a capacitor electrode 165 overlying the gate line 121 are formed on the ohmic contact layer 151, 152.
The data line 161, the source and drain electrodes 162 and 163, and the capacitor electrode 165 are covered with a passivation layer 170. The passivation layer 170 has first and second contact holes 171 and 172 exposing the drain electrode 163 and the capacitor electrode 165, respectively.
A pixel electrode 181 is formed at a pixel region on the passivation layer 170, the pixel region being defined by the gate line 121 and the data line 161 crossing the gate line 121. The pixel electrode 181 is electrically connected with the drain electrode 162 and the capacitor electrode 165 through the first and second contact holes 171 and 172.
The array substrate having the above construction can be fabricated by a photolithography process using five masks, where each process may include rinsing the substrate, coating a photoresist film, developing the exposed photoresist film and etching an exposed layer without the photoresist film.
Accordingly, if one photolithography process is omitted, the overall fabrication time is reduced to a considerable degree and the total fabrication cost can be decreased. Also, a substrate failure rate decreases. Therefore, it is preferable that the number of masks used be decreased during the fabrication of the array substrate.